Low cost virtual reality system

ABSTRACT

Apparatus is disclosed for viewing computer generated images and for tracking the positions of the user&#39;s head and hand. One alternative of the apparatus includes a frame element, versatilely mountable, with sensors for the head tracking of a user whose bodily movement is constrained to a small area. Short range and inexpensive sensors are deployed for tracking the position of the user&#39;s head; these sensors are deployed partly on a on the user&#39;s head and partly on the tracking frame. All the electronics for tracking and user input are enclosed in a mobile pack. In another alternative of the tracking invention natural forces such as gravity, the Earth&#39;s magnetic field, and inertia are used, so additional references. The display allows for interchangeable optical elements so that it may be tailored to suit the needs of a particular user or application. One optical element disclosed is a bicolor polarizer, which allows an lcd to inexpensively provide a bicolor display without loss of resolution.

This application is a divisional application of U.S. application Ser.No. 09/779,133, filed Feb. 7, 2001 U.S. Pat. No. 6,414,731, which is adivisional application of U.S. application Ser. No. 09/665,429, filedSep. 19, 2000 U.S. Pat. No. 6,452,514, which is a continuation of Ser.No. 09/118,734, filed Jul. 17, 1998, now U.S. Pat. No. 6,124,838, issuedSep. 26, 2000, which is a continuation of Ser. No. 08/319,026, filedOct. 6, 1994, now U.S. Pat. No. 5,850,201, which is a continuation ofabandoned U.S. application Ser. No. 08/165,045, filed Oct. 6, 1993,which is a continuation of abandoned U.S. application Ser. No.07/888,472, filed May 21, 1992, which is a continuation of abandonedU.S. application Ser. No. 07/621,127, filed Nov. 30, 1990.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of devices for dataentry, viewing, and manipulation in computers. More particularly, thisinvention relates to a low cost human interface system for interactivecomputer simulations, most particularly a low cost human interface for avirtual reality system.

Three of the key aspects of a virtual reality interface are tracking theuser's head and other body parts, sensing user input actions and displayof sensory information to the user in such a way that the sensoryinformation displayed replaces the corresponding senses arising from thephysical world. Such systems are typically quite expensive.

Position and orientation of the user's head and other body parts arecontinually tracked in order to keep the simulation updated tocorrespond correctly to the user's changing point of view. Trackingtechnologies have been relatively high cost components of a virtualreality system, and typically involve electromagnetictransmitter/receiver systems such as manufactured by Polhemus Inc., ofColchester, Ver.

The display of sensory information from the virtual reality simulationmust be proximal to the user's head at all times, so that the relativeposition of the display to the user's eyes and ears remains constant asthe user moves. Such a system is generally termed a Head Mounted Display(HMD), though it is not limited to devices mounted directly on the head.It contains visual and auditory displays for each sense organ and hastypically also been an expensive component.

Of particular interest here is the visual display portion of the HMD.Weight concerns generally dictate a liquid crystal display (lcd). Thegeneral structure of a lcd display includes a source of unpolarizedlight, a first polarizer, a polarization rotating array (which createsthe individual pixels), and a second polarizer which serves as ananalyzer. Light travels in the above named sequence. The first polarizergives the light a uniform polarization, either in the angle transmittedby the analyzer or perpendicular to it. The polarization rotating arrayoperates on the polarized light in a pixel-wise manner, either passingit unchanged or rotating the polarization by 90°. This light thencontinues on to the analyzer, which in one polarization angle transmitsall wavelengths, and perpendicular to that blocks all wavelengths, toleave light and dark pixels for display. Since in an HMD the pixels areso close to the viewer's eye, many people focus on the pixels at anindividual level and don't perceive the overall shapes within the imageas well. For this reason a diffusion screen may be superimposed over thelcd, which slightly blurs the image and fine detail, but facilitates theperception of patterns and shapes. Understandably, not all viewers likethis trade off.

Color lcds can be made by including a mask within the display, dyed withred, blue and green pixel sized dots. This mask is lined up with thepixels of the polarization rotating array, and each grouping of threemonochromatic pixels masked to form a red, blue and green pixel thenforms a color pixel. This conversion to a color lcd obviously results ina 3:1 reduction in resolution.

Color versus resolution is just one of the many trade-offs that must beresolved in choosing a display. Another important consideration iswhether and how much the fields of view of the right and left eyesoverlap. The most natural classification is into two groups—separateimages for each eye and totally shared images. Using separate images foreach eye instead of a totally shared image has the advantage of allowingstereoscopic vision and improved depth perception. Unfortunately, havingtwo separate images requires more computing power, and for an lcd ofgiven pixel size and distance from the eye only half as many pixels areavailable for each image, resulting again in lower resolution.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for viewingcomputer generated images with a variety of display characteristicseasily modifiable and with a high resolution bicolor lcd available, andfor inexpensively tracking the positions of the user's head and hand.

The tracking invention in one alternative includes a frame element forthe head tracking of a user whose bodily movement is constrained to asmall area. In a particular embodiment the tracking frame is mountableon a chair, in which the user would sit. Short range and inexpensivetracking elements are deployed for tracking the position of the user'shead; these tracking elements are deployed partly on the user's head andpartly on the tracking frame. The electronics for tracking and userinput are enclosed in a mobile pack, placed near the user or affixed tothe chair. In another particular embodiment, some of the hand trackingelements are located near the head, and hand tracking is referenced fromthe head. This limits the range of hand tracking to an arm's lengthradius, which further simplifies the electronics and processinginvolved. In yet another alternative of the tracking invention sensorsare employed which use natural forces such as gravity, the Earth'smagnetic field, and inertia as their reference, so additional referencesare unnecessary. In a particular embodiment of the invention directed tothe display, the head mounted display allows for interchangeable opticalelements so that the display characteristics may be tailored to suit theneeds of a particular user or application. One optical element disclosedis a bicolor polarizer which allows an lcd to inexpensively provide abicolor display without loss of resolution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a particular embodiment of a virtualreality system.

FIG. 2 is a side perspective view of a particular embodiment of atracking hood according to the present invention.

FIGS. 3a, 3 b and 3 c illustrate a particular embodiment of acollapsible tracking hood according to the present invention.

FIG. 4 illustrates a particular embodiment of the Head Mounted Displaywith bar coding for optical tracking of the head's yaw and pitch.

FIG. 5 is a spring loaded frame with interchangeable optical elementsfor use in an HMD.

FIG. 6 illustrates the effect of a bicolor polarizer on light.

FIGS. 7a and 7 b are particular embodiments of the tracking frame.

FIG. 8 is an alternative embodiment of the tracking frame.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 is a block diagram of a virtual reality system, and FIGS. 2through 5 of the drawings depict various particular embodiments of thepresent invention for purposes of illustration only. One skilled in theart will recognize from the following discussion that alternativeembodiments of the structures and methods illustrated herein may beemployed without departing from the invention.

Reference to FIG. 1 is helpful for an understanding of the presentinvention. World Model 10, information which is stored in a storagedevice such as magnetic disk or an interchangeable ROM cartridge, islinked to the Interaction Decision and Control Module (IDCM) 20, whichincludes a host computer and appropriate software. IDCM 20 in turn islinked to the Video Rendering Subsystem 30 and Audio Rendering Subsystem40, which typically comprise special coprocessors. These two renderingsubsystems 30 and 40 are also linked to the Video and Audio DisplaySubsystem (VADS) 100, which generally includes a Head Mounted Display(HMD) and appropriate drivers. The visual display portion of the HMD isusually an lcd; but in some particular embodiments is a liquid crystalshuttered (LCS) crt (LCSs are available from Tektronix, Inc. ofBeaverton, Oreg.), and in alternative particular embodiments is aPrivate Eye (available from Reflection Technology, Waltham Mass.).Tracking Subsystem (TS) 200 and User Input Subsystem (UIS) 300 areclosely related and both provide information to IDCM 20: TS 200 isresponsible for tracking the position and/or orientation of the user'shead and other body parts, whereas UIS 300 is responsible for moreconscious forms of input from the user, such as through DataGloves,DataVests, DataSuits, or a variety of other devices including eyetracking devices, voice recognition devices, video tracking devices,keyboards and other conventional data entry devices, pneumatic devices(oral sip and puff), facial expression sensors (optical, fiberoptic,electromyometric), sensors for biological data such as temperature,heart rate or blood pressure, joysticks, pressure sensitive floormats,etc. One example of a virtual reality system can be found in U.S. patentapplication Ser. No. 535,253 filed Jun. 7, 1990 entitled Virtual RealityNetwork incorporated herein by reference.

In a particular embodiment of the present invention as directed totracking, VADS 100, TS 200 and UIS 300 are closely linked physically, soa dotted line has been drawn around them in FIG. 1. FIG. 2 illustrates akey feature of TS 200 in this embodiment, which is a tracking frameformed as hood 210. Tracking hood 210 is shaped to partially surroundthe user's head, and it may be used to limit the freedom of movement ofthe user's head so that shorter range tracking sensors may be used.Position tracking elements are disposed on the hood and on the user'shead. The particular embodiment shown in FIG. 2 employs transmitter 220and receivers 230 and tracking is performed as described in U.S. patentapplication Ser. No. 317,107, entitled Computer Data Entry andManipulation Apparatus, incorporated herein by reference and commonlyowned. The close proximity of the position tracking elements on theframe to the position tracking elements on the head allow the use of anyvariety of optical, infrared, or ultrasonic short range inexpensivesensors known to those skilled in the art. In embodiments where HMD 110is strapped to the user's head, the tracking elements disposed on thehead are preferably incorporated into the HMD. In an alternativeembodiment the head tracking is done through spring loaded strings onpulleys disposed on the frame and attachable to a mounting on the user'shead. Potentiometers or shaft encoders within the pulleys thenaccurately and inexpensively track the head's movements. In a particularembodiment of the present invention directed to the hand trackingsystem, such is achieved through similar spring loaded string pulleysincorporated into the head tracking frame, which further simplifies thetracking and input process.

FIG. 4 illustrates another embodiment of the head tracking system, wherea counterbalanced HMD 110 includes bar coded strips 225 and 226 whichare read by optical sensors on the tracking hood for measuring thehead's pitch (rotation about the left-right horizontal axis) and yaw(rotation about a vertical axis). Limiting tracking to the head's pitchand yaw allows the use of very inexpensive sensors and greatlysimplified software. In an embodiment with even cheaper graphics theuser's virtual viewpoint is kept eye-level with the horizon and objectsare arranged to straddle the horizon. Only the head's yaw is tracked, sorelatively few views of the object may be perceived. Only image scalingand block image transferring (blitting) are necessary, resulting ingraphics that can be handled by an inexpensive processor.

Further alternative embodiments are shown in FIGS. 7a, 7 b and 8. FIG.7a shows frame 240 with support members 216, sensors 230, backing 212,and clamps 216. FIG. 7b shows frame 250, similar in design but withstand 217 for resting on a desk or similar structure. FIG. 8 showsportable frame 260, which dismantles into hollow rods 263, connectors261, 262, and elastic retaining cords 264. Sensors 230 respond to headtracking transmitter 265 and hand tracking transmitter 266.

Other alternative embodiments of the head tracking system do not requirea tracking frame, but instead use natural forces present in the world asreferences. The sensors for these embodiments are disposed on theperson's head. One such alternative embodiment employs tilt sensors(available from Technical Designs, Inc. of Seattle, Wash.), which usegravity as a reference and provides the head's yaw and pitch. Anotheralternative embodiment employs electronic compasses and provides thehead's yaw. Yet another alternative embodiment employs accelerometersand with appropriate software provides the head's x, y and z coordinatesrelative to the starting position, as well as yaw, pitch and roll. Aparticular embodiment of the invention directed to yaw-only tracking(for blit graphics), as mentioned above, employs an electronic compassfor head yaw tracking. Another particular embodiment of the presentinvention as directed to hand tracking systems employs accelerometers ona glove for hand tracking.

FIGS. 3a, 3 b and 3 c illustrate a particular embodiment of the headtracking system: collapsible tracking hood 210, with clasps 211 suitablefor mounting onto a chair, and support frame 212. Arcuit members 213 arecovered by sheath 214 and pivot at a common point so they may collapsetogether. Sheath 214 is opaque to reduce ambient light which mightinterfere with optical head tracking systems. For different mountingpurposes, different clasps can be used instead of those shown.

An embodiment of the invention directed to the display involves the HMDand is illustrated as display element 119 in FIG. 5. FIG. 5 shows frame120, which is part of the HMD and is positioned between the lcd and theuser's line of sight. Expandable frame 120 holds various opticalelements which may be interchanged; it includes front retaining bezel121 towards the user's eyes and rear retaining bezel 122 towards the lcdelements, connected by spring loaded connectors 123 so that it mayexpand to accommodate the selected optic elements. Element 130 replacesthe analyzer of the lcd and is an interchangeable polarizer; it may be anormal monochrome analyzer, a color masked analyzer, or a bicoloranalyzer as described below, whichever better suits the user or virtualenvironment. Interchangeable filter 140 may be a diffusion screen orother optical element desired by the user. Interchangeable lens 150allows modification from application to application of whether both eyeshave separate images or share the same one. The selection of lens 150also determines the angle which the image subtends on the user's eye,allowing adjustment of the angular resolution versus the angular fieldof view. In a particular embodiment of this invention theinterchangeable optical elements are coded so that IDCM 20 and VADS 100may automatically account for the selected display characteristics.

In a particular embodiment of the present invention directed to amulticolored display, an lcd is used wherein the second polarizer is abicolor polarizer. Alternatively, the first polarizer may be a bicolorpolarizer and the second polarizer a normal polarizer. A bicolorpolarizer is made of two colored polarizing swatches, each of whichtransmits all wavelengths in one polarization angle but only onewavelength, or a limited range of wavelengths, perpendicular to that(such polarizers are available in a variety of colors from SanritsuElectric Co., Habashi-Ku, Tokyo, Japan). These two swatches are placedwith their selective transmission axes perpendicular to each other, sothat at one polarization angle light of one frequency is transmitted andat a second polarization angle perpendicular to the first, light of asecond frequency is transmitted. FIG. 6 illustrates this operation:incoming white light has components in the α direction (angle), and inthe β direction (angle). Colored polarizer 101 passes all light in the αdirection, but blocks everything but green light in the β direction.This light continues to colored polarizer 102 which passes everything inthe β direction and blocks everything but red in the α direction. Theresulting light has only red light in the α direction (angle), and onlygreen light in the β direction (angle). Used as one of the polarizers ofan lcd, this results in a red against green display.

In an embodiment of the present invention directed to tracking, theclose interaction between the VADS 100, TS 200 and UIS 300 is aided byplacing all electronics for these subsystems in a mobile unit which maybe placed near the tracking hood and connected to it by cable. Thisclose placement increases speed of operation and reduces noise. Unitizedenclosure allows cost reduction, through shared electronics. In aparticular embodiment this mobile unit is housed within a backpack uponwhich the tracking hood is mountable.

The foregoing is the description of particular embodiments of theinvention. It should be understood that specific details, such ascomponent types, have been provided to explain the construction of theinvention. The scope of the invention may be determined from theappended claims.

We claim:
 1. A device for providing interchangeable optic elements foruse in a display unit of a virtual reality system comprising a) anexpandable frame including 1) a front retaining bezel; 2) a rearretaining bezel; and 3) means for urging the front retaining bezel andthe rear retaining bezel together; and b) at least one optic elementwhich fits inside the expandable frame.
 2. The device of claim 1,wherein the means for urging the front retaining bezel and the rearretaining bezel together comprises spring loaded connectors.
 3. Thedevice of claim 1, wherein the means for urging the front retainingbezel and the rear retaining bezel together comprises spring loadedconnectors, and wherein the spring loaded connectors are configured toassist in retaining at least one optic element between the front andrear retaining bezels.
 4. The device of claim 1, wherein the at leastone optic element comprises a monochrome analyzer.
 5. The device ofclaim 1, wherein the at least one optic element comprises a color maskedanalyzer.
 6. The device of claim 1, wherein the at least one opticelement comprises a bicolor analyzer.
 7. The device of claim 1, whereinthe at least one optic element comprises a filter.
 8. The device ofclaim 1, wherein the at least one optic element comprises a diffusionscreen.
 9. The device of claim 1, wherein the at least one optic elementis configured to facilitate adjustment of the angular resolution versusthe angular field of view.
 10. The device of claim 1, wherein the atleast one optic element comprises a coding means configured tofacilitate a control means to identify the at least one optic elementduring use.
 11. A display apparatus suitable for use in a virtualreality system, comprising a) a light source; b) a first polarizeroptically coupled to the light source; c) a polarization rotating arrayoptically coupled to the first polarizer; d) an expandable frame forholding interchangeable optic elements, positioned so that selectedoptic elements are operably coupled to the polarization rotating array,including 1) a front retaining bezel; 2) a rear retaining bezel; and 3)means for urging the front retaining bezel and the rear retaining bezeltogether; and e) at least one lcd analyzer suitable for being insertedinto and removed from the expandable frame; and f) at least one lenssuitable for being inserted into and removed from the expandable frame.12. The apparatus of claim 11, wherein the means for urging the frontretaining bezel and the rear retaining bezel together comprises springloaded connectors.
 13. The apparatus of claim 11, wherein the means forurging the front retaining bezel and the rear retaining bezel togethercomprises spring loaded connectors, and wherein the spring loadedconnectors are configured to assist in retaining the optic elementbetween the front and rear retaining bezels.
 14. The apparatus of claim11, wherein the means for urging the front retaining bezel and the rearretaining bezel together comprises spring loaded connectors, and whereinthe spring loaded connectors are configured to assist in retaining theat least one lens between the front and rear retaining bezels.
 15. Theapparatus of claim 11, wherein the optic element comprises a filter. 16.The apparatus of claim 11, wherein the optic element comprises adiffusion screen.
 17. The apparatus of claim 11, wherein the at leastone optic element is configured to facilitate adjustment of the angularresolution versus the angular field of view.
 18. The apparatus of claim11, wherein the at least one lens comprises a coding means configured tofacilitate a control means to identify the at least one lens during use.19. The apparatus of claim 11, wherein the optic element comprises acoding means configured to facilitate a control means to identify theoptic element during use.
 20. A device for providing interchangeableoptic elements for use in a display unit of a virtual reality systemcomprising: an expandable frame comprising: a front retaining bezel; arear retaining bezel; and a spring loaded connector configured to assistin retaining at least one optic element between the front and rearretaining bezels; and at least one optic element which fits inside theexpandable frame.
 21. The device of claim 20, wherein the at least oneoptic element comprises a monochrome analyzer.
 22. The device of claim20, wherein the at least one optic element comprises a color maskedanalyzer.
 23. The device of claim 20, wherein the at least one opticelement comprises a bicolor analyzer.
 24. The device of claim 20,wherein the at least one optic element comprises a filter.
 25. Thedevice of claim 20, wherein the at least one optic element comprises adiffusion screen.
 26. The device of claim 20, wherein the at least oneoptic element is configured to facilitate adjustment of the angularresolution versus the angular field of view.
 27. The device of claim 20,wherein the at least one optic element comprises a coding meansconfigured to facilitate a control means to identify the at least oneoptic element during use.
 28. A display apparatus suitable for use in avirtual reality system, comprising: a light source; a first polarizeroptically coupled to the light source; a polarization rotating arrayoptically coupled to the light source; a polarization rotating arrayoptically coupled to the first polarizer; a frame for holdinginterchangeable optic elements, position so that selected optic elementsare operably coupled to the polarization rotating array; at least onelcd analyzer suitable for being inserted into and removed from theexpandable frame; and at least one lens suitable for being inserted intoand removed from the expandable frame.
 29. The apparatus of claim 28,herein the optic element comprises a filter.
 30. The apparatus of claim28, wherein the frame is expandable, and wherein the frame comprises: afront retaining bezel; a rear retaining bezel; and a spring loadedconnector configured to assist in retaining at least one optic elementbetween the front and rear retaining bezels.
 31. The apparatus of claim28, wherein the frame is expandable.
 32. The apparatus of claim 28,wherein the optic element comprises a diffusion screen.
 33. Theapparatus of claim 28, wherein the at least one optic element isconfigured to facilitate adjustment of the angular resolution versus theangular field of view.
 34. The apparatus of claim 28, wherein the atleast one lens comprises a coding means configured to facilitate acontrol means to identify the at least one lens during use.
 35. Theapparatus of claim 28, wherein the optic element comprises a codingmeans configured to facilitate a control means to identify the opticelement during use.